The coding of olfactory information begins with an animal's ability to detect and discriminate odorants. In the mouse olfactory system this is accomplished by a family ofapproximately 1000 functional odorant receptor genes each of which is expressed in thousands of neurons. A mature olfactory neuron expresses only 1 odorant receptor gene from only 1 allele. Odorant receptors (OR) are critical for the convergence of thousands of identical axons into 2 symmetrically located glomeruli on an olfactory bulb thereby creating approximately 2000 glomeruli. The marriage of mouse genetics and neural development has allowed for molecular dissection of these processes. This project continues with the analysis of the mouse olfactory system. In Aim 1, the temporal development will be determined for 2 highly related ORs that correspond to spatially related positions on the surface of the olfactory bulb. This analysis will determine if the onset of glomerular formation correlates with its final position on the olfactory bulb. A parallel study will determine if altering the number of axons for a given axonal population affects its position of convergence. In Aim 2, polymorphic OR proteins will probe if domains in the OR impart specificity to axons that converge into glomeruli. These experiments will provide a foundation for how olfactory glomeruli develop. Results generated will elaborate whether there are intrinsic positions on the olfactory bulb that are laid down by gradients and if there is an under appreciated plasticity in the olfactory system. The process by which olfactory sensory neurons are constantly re-establishing codes of connectivity to the olfactory bulb, may give insights into axonal pathfinding in other regions of the brain. [unreadable] [unreadable]